There were two kinds of blacklists operating in the Hollywood of the anti-red 1950s – the overt one, where people were brought before the House UnAmerican Activities Committee – and the covert one, the "grey list", where work was hard to find. Maxine Cooper, who has died aged 84, was a victim of the latter.

From her early career, Cooper was an outspoken advocate of peace and nuclear disarmament, not a position to endear her to the conservative Hollywood establishment. Furthermore, she had a son out of wedlock (father unrevealed) in 1952, a definite no-no. No other reasons explain why a talented, intelligent, attractive woman such as Cooper had only one substantial role in a feature throughout the whole decade.

That key role was as Velda, sexy secretary to the hardboiled private eye Mike Hammer in Robert Aldrich's Kiss Me Deadly (1955), a multi-layered film noir that used a Mickey Spillane pulp novel as the basis for a gripping allegory of cold war paranoia. The plot involved Hammer (Ralph Meeker) and Velda's search for a mysterious black box, which she calls the "great whatsit", sought after by a foreign power and racketeers. In the finale, the radioactive box is opened at a beach house and everything goes up in flames while Hammer and Velda escape into the sea. Another ending, circulated for years, showed a conflagration with no survivors. This cut was thought more moral by United Artists executives.

Happily, the original version has since been restored. "That's the way it was shot … the idea being that Hammer was left alive long enough to see what havoc he had caused, though certainly he and Velda were both seriously contaminated," explained Aldrich.

The sado-masochistic relationship between Velda and Hammer has Cooper and Meeker playing off each other brilliantly. She is devoted to him, although he is a narcissistic bully. "You're never around when I need you," he tells her. "You never need me when I'm around," she replies.

When Hammer's friend is killed, she recognises his mercenary intentions: "You want to avenge the death of your dear friend. How touching. How sweet. How nicely it justifies your quest for the great whatsit."

Born in Chicago, Cooper became interested in acting at Bennington, in Vermont, a liberal arts college for women. She completed her dramatic training at the Pasadena Playhouse before going to Europe in 1946 to take part in shows for soldiers. She stayed for five years, appearing in the American Theatre in Paris and in several BBC television productions, including The Front Page (1948), in which she played the waiting fiancee of reporter Hildy Johnson, played by Sid James.

Returning to the US, she had a number of good theatre parts, one of them in a Los Angeles production of Ibsen's Peer Gynt, in which she was spotted by Aldrich. In 1955, the same year as the release of Kiss Me Deadly, Cooper was seen in several television series, including Alfred Hitchcock Presents, but there were no further Hollywood offers. Only her friend Aldrich managed to give her small parts in two of his films, Autumn Leaves (1956) and Whatever Happened to Baby Jane? (1962), both starring Joan Crawford. In 1957, Cooper married screenwriter-producer Sy Gomberg, with whom she had two daughters, thereafter trimming TV work.

However, Cooper, with her husband, continued her political activism. They were supporters of the American Civil Liberties Union and went on a civil rights march with Martin Luther King in Alabama, and participated in protests against the Vietnam war and nuclear weapons. She was also a keen photographer and her photos (as Maxine Gomberg) illustrate the Howard Fast book The Art of Zen Meditation (1977).